protection for those species that are covered by the plan, but receive no protective measures

Habitat conservation plans are intended to achieve a balance between development and the long-term conservation of species listed as endangered or threatened under the Endangered Species Act. Developers seeking permits for the incidental take of listed species often include multiple species in their plans, both listed and nonlisted, because if a species not in the plan is subsequently listed under the act, the continued activities of the permittee could be jeopardized.

[The study] analyzed 22 multispecies plans approved by the US Fish and Wildlife Service before 2005. On average, 41 percent of the species covered in the plans had not been confirmed as present in the planning area, a finding the authors describe as "alarming." Furthermore, most of these unconfirmed species lacked any species-specific conservation measures, which means that a multispecies habitat conservation plan could represent a danger.

Rahn and colleagues argue that "assumptions of occurrence should be justified" in multispecies conservation plans. They suggest that the US Fish and Wildlife Service has been inclined to issue permits for multispecies conservation plans in the absence of data, relying instead on professional judgment. Rahn and colleagues call that a "dangerous practice" and suggest that it may help explain why species in multispecies habitat conservation plans fare poorly compared with species with dedicated plans.

Multispecies habitat conservation plans that permit the incidental "take" of threatened or endangered species often include species whose presence in the planning area has not been confirmed... The result, the article argues, is that some species that are present but unconfirmed are placed in greater danger.